A test on the electrical characteristics of a device such as a semiconductor memory and an integrated circuit formed on the semiconductor wafer is performed by using a probe device. The probe device typically includes an inspection unit for performing a test of the semiconductor wafer and a loader unit provided adjacent to the inspection unit. In the inspection unit, a low temperature test or a high temperature test may be performed in a state where the semiconductor wafer has been cooled or heated, in addition to a room temperature test. The loader unit includes an accommodation unit which accommodates a cassette containing a plurality of semiconductor wafers, and a transfer device having a plurality of transfer arms for transferring the semiconductor wafers between the cassette and the inspection unit. The transfer device unloads the semiconductor wafer from the cassette by using the transfer arm and transfers the semiconductor wafer to the inspection unit. Further, the transfer device receives an inspected semiconductor wafer from the inspection unit and transfers the inspected semiconductor wafer to an original place in the cassette.
When the low temperature test is performed, the semiconductor wafer is cooled to minus several tens of degrees in the inspection unit maintained in a low dew point environment. When the low temperature test in the inspection unit is completed, the inspected semiconductor wafer is unloaded from the inspection unit by the transfer device and returned into the cassette of the loader unit. At this time, if condensation or congelation occurs in the semiconductor wafer during the transfer of the semiconductor wafer from the inspection unit to the cassette of the loader unit or in the semiconductor wafer within the cassette, this may cause a deffect in the device formed on the semiconductor wafer. In order to prevent such condensation and congelation after the low temperature test, there has been suggested a technique that provides a shield container for covering the transfer arm and a unit for supplying a dry gas into the shield container (see, e.g., Japanese Patent No. 3783075).
Recently, in order to rapidly perform a test with respect to a plurality of semiconductor wafers, there has been suggested an inspection system including a loader unit in which a plurality of cassettes can be installed and a plurality of test devices (see, e.g., Japanese Patent Application Publication No. 2013-254812). The inspection system is configured to transfer the semiconductor wafer between the test devices and the cassettes.
In a probe device disclosed in Japanese Patent Application Publication No. 3783075, the semiconductor wafer is transferred between one inspection unit and the cassette of the loader unit. While a new semiconductor wafer is being inspected, a semiconductor wafer that has been inspected just before the inspection of the new semiconductor wafer may stand by on the transfer arm of the transfer device for a predetermined period of time. During this standby status, a dry air is supplied into the shield container to prevent condensation and congelation in the semiconductor wafer. Moreover, by providing a sufficient standby time, a temperature of the inspected semiconductor wafer can be increased to a temperature level at which condensation and congelation does not occur, when the semiconductor wafer is delivered to the cassette.
In the inspection system having the test devices disclosed in Japanese Patent Application Publication No. 2013-254812, in order to improve a throughput, it is important to extremely reduce an idle time of the transfer devices. Specifically, in the above inspection system, it is required that the inspected semiconductor wafer is instantly unloaded from the test device, exchanged with an uninspected semiconductor wafer, and rapidly delivered to the loader unit, and the inspection system is prepared for the transfer of another semiconductor wafer. For this reason, in the above inspection system, when the low temperature test is performed, it is difficult to secure a suifficient standby time on the transfer arm for preventing condensation and congelation in the semiconductor wafer. Further, this problem becomes more difficult to be solved as the number of the test devices that are transfer destinations increases. That is, when the low temperature test is performed in the inspection system having a plurality of test devices, a conventional method is insufficient to effectively prevent condensation and congelation that occur during the transfer. Accordingly, a new method is required.